The present invention relates to a ink-jet print head and ink-jet printer which prevents bubbles from being trapped within the ink supply passage of an ink-jet head preventing ink from flowing smoothly and being normally jetted from the ink nozzles, and which prevents crosstalk from occurring when vibration due to pressure is caused in the ink supply passage, resulting in fluctuation in the ink jetting speed and preventing ink from being driven from the ink nozzles.
FIG. 1 shows a typical cross-sectional composition of a conventional ink-jet print head 1. A nozzle plate 2 in the front of the head 1 is provided with multiple ink jetting nozzles 3 arranged in a direction which lies perpendicular to the page. Multiple pressure chambers 5, also arranged in a direction perpendicular to the page, and respectively communicating with each nozzle 3, and a common ink reservoir 7 (extended along the direction perpendicular to the page, along the line of the pressure chambers 5) for supplying ink to each pressure chamber 5, are provided to the rear of the nozzle plate 2. An ink supply passage 9 for carrying ink from an ink cartridge (not shown) is connected to the ink reservoir 7 through the casing 11 of the head 1. Normally, the ink supply passage 9 is connected to the center of the ink reservoir 7 which is extended along in the direction perpendicular to the page.
The rear surface of each pressure chamber 5 and the ink reservoir 7 is covered with a flexible or an elastic film 13, and a rigid reinforcing plate 15, such as a stainless steel plate, is laminated on the film 13. FIG. 2 is a sectional view showing the reinforcing plate 15 viewed along a line Axe2x80x94A in FIG. 1. (The cross-section of the head shown in FIG. 1 is viewed along a line Bxe2x80x94B in FIG. 2.) As shown in FIG. 2, plural apertures 17, 19, and 21, are formed inside the reinforcing plate 15 by etching. The rectangular aperture 17 is provided at the rear of the line of pressure chambers 5, the circular hole 19 in the center of the plate 15 corresponds to the exit to the reservoir 7 of the ink supply passage 9, and the wing-type apertures 21 on both sides of the circular hole 19 is provided at the rear portion of the plate 15, except for the center of the reservoir 7. Multiple rectangular insulating parts 18 existing inside the rectangular aperture 17 are respectively located at the rear of the individual pressure chamber 5.
Referring to FIG. 1 again, each end of the parts in the shape of the teeth of a comb divided into multiple parts of a piezoelectric element 23, is bonded to the film 13 at the rear of each pressure chamber 5 via each insulating part 18 shown in FIG. 2. The piezoelectric element 23 is fixed to the casing 11, the film 13 of each pressure chamber 5 is reciprocated because each part like a tooth of a comb of the piezoelectric element 23 is expanded or contracted according to a signal from a cable 25, and pressure is generated in each pressure chamber 5 and ink is jetted from each nozzle 3. Simultaneously, ink is also jetted from the pressure chamber 5 into the reservoir 7; however, the film 13 covering the rear surface of the reservoir 7 absorbs the pressure of the jet.
Bubbles may be included in ink which flows from the ink cartridge to the reservoir 7 through the supply passage 9. The bubbles may grow to a size equal to the diameter of the supply passage 9 in the worst case, and such a large bubble may be trapped in the vicinity of a connection between the supply passage 9 and the reservoir 7 and may remain there. As a result, ink does not flow smoothly and ink cannot be normally jetted from each nozzle 3.
When ink is jetted, an ink jet from the pressure chamber 5 functions as a trigger in the reservoir 7, and an MC circuit composed of the compliance C of the film 13 at the back of the reservoir and the inertance M of the ink supply passage 9 is oscillated, and vibration due to pressure may be caused. As a result, a problem called crosstalk, such as the fluctuation of the ink jetting speed and the jet of ink from the nozzle 3 being not driven, is caused.
It is when a nozzle 3 in the vicinity of the center of a nozzle train is driven that crosstalk is easily caused. The reason is as follows: in this case, ink is jetted from the pressure chamber 5 in the vicinity of the center to the center of the reservoir 7, that is, the vicinity of a connection between the reservoir and the ink supply passage 9. However, as the rear surface in the vicinity of the center of the reservoir 7 is covered with the peripheral part 15A (a required location for bonding to the peripheral part of the exit of the ink supply passage 9) of the exit hole 19 of the ink supply passage 9 inside the reinforcing plate 15 as shown in FIG. 2, a jet of ink is trapped. Therefore, a problem that a high-pressure wave is generated in the center and is propagated to the periphery, and ink is jetted from a nozzle from which ink is not to be jetted, is caused.
Therefore, the object of the present invention is to prevent bubbles from remaining in an ink passage of an ink-jet print head.
Another object of the present invention is to inhibit crosstalk when ink is jetted.
An ink-jet print head according to one standpoint of the present invention is provided with a plurality of ink jetting nozzles arranged in line, a plurality of pressure chambers respectively communicating with each nozzle and arranged in line, an ink reservoir extended along the line of the pressure chambers and communicating with the pressure chambers in common and provided with a predetermined width and depth, and an ink supply passage communicating with the ink reservoir. The diameter of the ink supply passage is reduced at the exit to the ink reservoir, compared with the part of the ink supply passage on the upstream side of the exit.
According to the above ink-jet print head, as the flow velocity of ink is increased at the exit of the ink supply passage where the diameter is reduced, bubbles are easily pushed out and as bubbles are reduced, few bubbles remain.
In a preferred embodiment, the width at the exit of the ink supply passage is made smaller than the width and depth of the ink reservoir. Thereby, bubbles can more easily pass the ink reservoir and the effect of preventing bubbles from remaining in the ink supply passage is further enhanced. It is desirable that the width of the ink reservoir is larger than the depth.
Also, in the preferred embodiment, the exit of the ink supply passage is arranged at an edge on the reverse side to the side of the pressure chamber in the center of the ink reservoir, in a direction along the line of the pressure chambers, and the width at the exit of the ink supply passage is smaller than the width of the ink reservoir. Therefore, the exit of the ink supply passage is located off an area in the vicinity of the pressure chamber of the ink reservoir. The area in the vicinity of the pressure chamber of the ink reservoir is covered with a flexible film in a state in which the film is deformable and the area covered with the film continues in an overall range from one end along the line of the pressure chambers to the other end. According to the above arrangement, the pressure of an ink jet from any pressure chamber is effectively absorbed by the flexible film and crosstalk is reduced.
To reduce crosstalk, it is desirable that the compliance of the flexible film covering the ink reservoir is large and the inertance of the ink supply passage is small. From this viewpoint, it is desirable that the width of the ink reservoir is larger than the depth, and that the diameter of the ink supply passage in the part except the exit, is thicker than the diameter at the exit.
An ink-jet print head according to a second embodiment of the present invention, includes a plurality of ink jetting nozzles arranged in line, a plurality of pressure chambers respectively communicating with each nozzle and arranged in line, an ink reservoir extended along the line of the pressure chambers and communicating with the pressure chambers in common and provided with a predetermined width and depth, a flexible film covering at least a part of the outer surface of the ink reservoir in a deformable state and an ink supply passage communicating with the ink reservoir. An area in which the flexible film covers the ink reservoir in a deformable state continues at least from one end of the line of the pressure chambers to the other end in the vicinity of the pressure chamber along the line of the pressure chambers.
An ink-jet print head according to a third embodiment of the present invention is provided with a plurality of ink jetting nozzles arranged in line, a plurality of pressure chambers respectively communicating with each nozzle and arranged in line, an ink reservoir extended along the line of the pressure chambers and communicating with the pressure chambers in common and provided with a predetermined width and depth, and an ink supply passage communicating with the ink reservoir. The exit of the ink supply passage is arranged on the reverse side to the side of the pressure chamber in the center of the ink reservoir.
An ink-jet print head according to a fourth embodiment of the present invention is provided with a plurality of ink jetting nozzles arranged in line, a plurality of pressure chambers respectively communicating with each nozzle and arranged in line, an ink reservoir extended along the line of the pressure chambers and communicating with the pressure chambers in common and provided with a predetermined width and depth, an ink supply passage communicating with the ink reservoir, and a flexible film for covering at least a part of the outer surface of the ink reservoir in a deformable state and acting so that the pressure of a jet of ink from each of the pressures chamber into the ink reservoir is absorbed thereby. The exit of the ink supply passage is arranged on the reverse side to the side of the pressure chamber in the center of the ink reservoir in a direction along the line of the pressure chambers, and the width at the exit of the ink supply passage is smaller than the width of the ink reservoir. Further, an area in which the flexible film covers the ink reservoir in a deformable state continues at least from one end of the line of the pressure chambers to the other end in the vicinity of the pressure chamber along the line of the pressure chambers.
According to the above ink-jet print head, the pressure of an ink jet from any pressure chamber is effectively absorbed by the flexible film and crosstalk is reduced.
The present invention further also provides an ink-jet printer provided with an ink-jet print head provided with the above structure, a carriage mechanism for moving the ink-jet print head, a paper feed mechanism for feeding paper, and a control circuit for driving and controlling these mechanisms.